A、Their similar social status. B、Their interdependence. C、Their common interest. D、Their identical character. C

We don’t choose friends on the basis of how much money they have, of course, but vast differences can be disturbing to both sides. Erin, for example, is single, and earns a very good salary. Her friend, Pat, a divorced mother of three, is struggling to make ends meet. " We are both frequent theater-goers," Erin explains, " and I’d gladly pay for two tickets, just to have pat’s company at plays in concerts , but she won’t go anywhere unless she can pay her own way. I hate to go alone, so we both stay home. It all seems so silly. " Pat sees the situation differently. After her unhappy marriage to a man who tried to control her without considering her wishes and feelings, she says, " It’s very important to me to carry my own weight. I’m not comfortable in any relationship where all I do is take.
    The difficult situation finally changed when Erin moved recently. Pat’s children were with their father, so she took a picnic lunch to her friend’s new plays, then spent the day helping her unpack and get settled. "I was so grateful, " Erin says, " that I persuaded Pat to let me return the favor in my own way with season tickets to our little theater group. I think she’s beginning to recognize that she contributes as much to our friendship as I do"
16. What do we learn about Pat?
17. What draws Erin and Pat together?
18. What does Erin do to return Pat’s favor?
19. What do we learn about friendship from the passage?